1. Field of the Invention
The present invention relates to methods for use in an image processing system to enhance the overall picture quality of an electronically displayed picture.
2. Description of Related Art
Modem storage and transmission of pictures occurs by electronic means, in which analog electronic signals are converted to digital groups of numbers representing the total information necessary to re-create one picture element (one pixel) on a screen, such as a CRT screen or a plasma screen or a Liquid Crystal Display. Electronic picture may also originate in the digital domain. A picture is defined by many parameters, some of which are related to the human visual perception. Contrasts between series of neighboring pixels are perceived as contours, and correct representation of such contours as well as gradual changes in e.g. chromaticity are important elements in a high quality picture representation. In particular two influences occur that reduce the quality of the perceived image: noise that introduces random stepwise variation between neighboring pixels and data reduction algorithms that introduce “ringing” and “blocking”. The former refers to shadow- or ripple-like extraneous series of pixels in parallel with contrasts—in the case of lines, on both sides of the lines, and the latter refers to the generation of rectangular blocks of uniformly colored parts of a picture, which appears as if it were displayed on a tiled surface. Both phenomena may occur with varying degree of visibility. Typical present-day algorithms are of the family known as MPEG (Motion Picture Experts Group).
Various principles for reducing noise and artifacts have been used in the past, from simple averaging of the values of neighboring pixels to principles including movement information from consecutive frames in video. Reference is made to Anil Kokaram, “Motion Picture Restoration”, Springer Verlag London 1998. The sophisticated methods are both very complex, calculation-intensive, and require more hardware than it is generally considered reasonable to include in equipment for home entertainment, such as TV and video monitors or computer screens.